Removal of ferrous sulfate from nickel baths

ABSTRACT

PROCESS FOR THE REMOVAL OF FERROUS SULFATE FROM NICKEL PLATING SOLUTIONS WHICH INVOLVES ADDING HYDROGEN PEROXIDE TO THE SOLUTION AND ADJUSTING THE PH TO A VALUE OF ABOUT 3.1 TO 3.3 TO THEREBY PRECIPITATE FERRIC SULFATE IN A FORM WHICH CAN BE READILY REMOVED FROM THE REMAINDER OF THE SOLUTION BY FILTRATION.

United States Patent 3,578,469 REMOVAL OF FERROUS SULFATE FROM NICKELBATHS Richard N. Hudd, Wheaten, and Heinz Seller, Cicero,

Ill., assignors to Eagle-Picher Industries, Inc., Cincinnati, Ohio NoDrawing. Filed Mar. 24, 1969, Ser. No. 810,012

Int. Cl. C23c 3/02 U.S. Cl. 106-1 8 Claims ABSTRACT OF THE DISCLOSUREProcess for the removal of ferrous sulfate from nickel plating solutionswhich involves adding hydrogen peroxide to the solution and adjustingthe pH to a value of about 3.1 to 3.3 to thereby precipitate ferricsulfate in a form which can be readily removed from the remainder of thesolution by filtration.

BACKGROUND OF THE INVENTION Field of the invention This invention is inthe field of treating nickel plating solutions which become contaminatedwith ferrous sulfate as nickel plating proceeds, the treatmentconsisting of adding hydrogen peroxide to the solution at a controlledpH to thereby oxidize the ferrous sulfate toferric sulfate and provide aprecipitate which can be easily removed from the nickel plating bath bymeans of filtration.

Description of the prior art In Zander U.S. Pat No. 2,837,443 issuedJune 3, 1958 and assigned to the same assignee as the presentapplication, there is described a method of porcelain enameling whichpermits the direct on or single coat application of titania opacifiedporcelain enamels over ferrous substrates of various descriptions. Thistype of process involves first cleaning the piece one or more times withan aqueous alkaline cleaner containing sodium phosphate, sodiumcarbonate, sodium hydroxide, soaps, wetting agents and detergents. Thecleaning takes place at the boiling temperature of the cleaner, and thearticle remains immersed in the cleaner for ten to fifteen minutes ineach stage. Then, the cleaned article is rinsed with first warm and thencold water, after which it is pickled with a nitric acid solutioncontaining about 8 to nitric acid. After rinsing with running water, thearticle is then subjected to treatment with aqueous sulphuric acid andiron sulfide, the treating solution containing about 6.5 to 8.0%sulphuric acid, and 4 to 8 grams of iron sulfide per gallon of acidsolution. The temperature is maintained at about 180 F., and the articleremains immersed in the solution for four to five minutes.

After a succession of rinses with running water, the article is immersedin a bath of sodium cyanide having a concentration of about 1 ounce pergallon or so, and at a temperature of about 120 F. The immersion time isnormally two to three minutes in this stage. After another running waterrinse, the article is immersed in an aqueous bath of nickel sulfate fromwhich it receives a flash coating of nickel. The usual concentration ofnickel sulfate in this bath is about 1.5 ounces per gallon at atemperature of about 165 to 175 F. The pH is usually on the order of 3to 3.5. The article remains immersed in the bath for four to fiveminutes or so, whereupon it receives a nickel flash deposit ranging fromabout 0.05 to 0.12 gram per square foot.

The nickel deposition proceeds according to the ollowing equation:

3,578,469 Patented May 11, 1971 'ice Continued operation of the nickelplating bath increases the concentration of ferrous sulfate in the tank,whereupon the operation has to be stopped and the contents of the nickeltank dumped. As the ferrous sulfate concentration builds up, theefficiency of the nickel plating operation decreases. In addition, thepresence of ferrous sulfate results in building up iron scale in thetank, in spray nozzles, headers and other portions of the picklingmachine.

SUMMARY OF THE INVENTION The present invention provides a means ofremoving the detrimental effect of ferrous compounds in the nickelplating bath by oxidizing the same with hydrogen peroxide eithercontinuously or on an intermittent basis. The oxidation takes place whenthe pH of the nickel plating bath is maintained at a range of about 3.1to 3.3 through the addition of any of a variety of alkaline actingagents. The ferric sulfate which is formed precipitates cleanly from thenickel plating bath and can be removed without significant loss ofnickel values.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The ferrous sulfate in thenickel plating bath is oxidized to ferric sulfate according to thefollowing equation:

As the above reaction proceeds, the pH becomes more acid and approaches1.5. In order to bring the pH back to the desired range of 3.1 to 3.3,various alkaline acting materials can be used. For example, nickelcarbonate may be used in its anhydrous or hydrated form. In addition, analkali metal hydroxide such as sodium hydroxide or potassium hydroxidemay be used. An alkali metal carbonate including sodium carbonate andpotassium carbonate may similarly be employed. The hydroxides orcarbonates of alkaline earth metal such as barium and calcium are alsouseful for this purpose. Still another class of materials which can beused for securing the proper pH control are the alkali metal andalkaline earth metal peroxides, such as the peroxides of sodium,potassium, barium and calcium.

As mentioned previously, the hydrogen peroxide can be added continuouslyor intermittently as the nickel plating reaction proceeds. It is merelynecessary to maintain the proper molar concentrations for the reactionto proceed, namely, one molecular proportion of hydrogen peroxide forevery two molecular proportions of ferrous sulfate formed. The hydrogenperoxide can be added either as a dilute or as a concentrated solution.

The ferric sulfate which results from this reaction is a precipitatewhich is easily removed from the remaining solution by filtration. Ithas been found that the process of the present invention significantlyimproves the life of the nickel plating solution so that fairlyconcentrated nickel containing solutions need not be disposed of andcreate a pollution problem. Furthermore, the plating reaction occurs atmaximum efiiciency, without interference from the ferrous ions. Theremoval of iron in insoluble form reduces the possibility of building upiron scale in the equipment and reduces the maintenance problemsassociated with the pickling machine. It has also been found that withthe process of the present invention, a given thickness of nickeldeposit can be achieved at a reduced solution contact time. The normalnickel plating temperature of to F. can be employed for this reaction,so that there is no interference with the normal plating reaction byvirtue of the addition of hydrogen peroxide.

It should be evident that various modifications can be made to thedescribed embodiments without departing from the scope of the presentinvention.

We claim as our invention:

1. The method of treating a nickel plating solution containing nickelsulfate and sulphuric acid in amounts and under conditions conducive tothe continued formation of ferrous sulfate produced by immersing ferrousarticles in said solution for the oxidation and removal of ferroussulfate which comprises adding hydrogen peroxide to said solution in anamount sufficient to oxidize the ferrous sulfate to ferric sulfate, andadjusting the pH to a value in the range from about 3.1 to about 3.3with an alkaline acting agent to thereby cause precipitation of readilyfilterable ferric sulfate therein.

2. The method of claim 1 in which the pH is adjusted by the addition ofnickel carbonate to said solution.

3. The method of claim 1 in which the pH is adjusted by the addition ofan alkali metal hydroxide to said solution.

4. The method of claim 1 in which the pH is adjusted by the addition ofan alkali metal carbonate to said solution.

5. The method of claim 1 in which the pH is adjusted by the addition ofan alkaline earth hydroxide to said solution.

6. The method of claim 1 in which the pH is adjusted by the addition ofan alkaline earth carbonate to said solution.

7. The method of claim 1 in which the pH is adjusted by the addition ofan alkali metal peroxide to said solution.

8. The method of claim 1 in which the pH is adjusted by the addition ofan alkaline earth peroxide to said solution.

References Cited UNITED STATES PATENTS 3,265,511 8/1966 Sall 106-1LORENZO B. HAYES, Primary Examiner US. Cl. X.R. 117-130

